Summary

• continue validating later SQL columns when a nullable column is absent from the Avro schema
• add a regression covering a missing nullable column followed by a missing required column

Root cause

validate_struct_schema returned success for the entire record when it encountered one missing nullable column. This skipped validation of every subsequent column, allowing missing required or incompatible columns to pass startup validation and fail later while parsing data.

Impact

Missing nullable columns remain supported for schema evolution, while all other declared SQL columns are still checked for compatibility.

Validation

• cargo test -p dbsp_adapters format::avro:: --lib (46 passed on current upstream main)
• cargo test -p dbsp_adapters missing_nullable_field_does_not_stop_validation --lib (passed on the published fork branch)
• cargo fmt --all -- --check